1. Field of the Invention
The invention relates in general to an antenna device, and more particularly to a multiple-input multiple-output (MIMO) antenna device capable of adjusting the radiation pattern.
2. Description of the Related Art
Multiple-input multiple-output (MIMO) technology will become a mainstream technology in wireless communication in the future. Unlike conventional single antenna systems, many antennas are operated concurrently in MIMO systems, so that the data transmission in the wireless network is more stable and the data transmission rate is increased. At present, the MIMO technology has become standardized specification in communication protocols such as IEEE 802.11n (WiFi) and 802.16d/e (WiMAX). Recently, adaptive MIMO systems have been provided. The adaptive MIMO systems refer to systems that the coding method and the antenna characteristics are adjustable, so that the adaptive MIMO system is capable of achieving an optimum working mode according to the real-time state of wireless channels. Therefore, the design of antennas with adjustable radiation characteristics is essential in adaptive MIMO systems.
As too much space of a wireless communication product is occupied by one conventional antenna, it is very difficult to install many antennas whose radiation characteristics are adjustable. Thus, the antenna design is a bottleneck to break through for an electronic product to in-build many communication systems operated in different frequency bands and adopting the MIMO technology.
Accordingly, the MIMO antenna system whose size is small and the radiation characteristics are adjustable heralds whether future small-sized electronic devices can fully utilize the resources of the wireless network.